Mask for proximity field optical exposure, exposure apparatus and method therefor

ABSTRACT

A mask for exposure  1  having an aperture in a prescribed pattern formed on one surface and subjected to proximity field exposure in a state kept in contact with the surface of a wafer  2 . The mask  1  is made of a transparent material such as glass or quartz glass. The mask  1  forms a circular shape with a thickness of 1 mm or less, preferably 0.1-0.5 mm.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to a mask used for proximity field opticalexposure for duplicating a fine pattern (hereinafter referred to as“mask”), and in an application technical field, relates to formation ofa fine pattern which is applicable to a grating used as an opticalcircuit element such as a distributed feedback laser, for example, DFBand DBR.

[0003] 2. Description of the Related Art

[0004] Development of optical lithography has been supported by theprogress of a reduced projection exposure technique and a photoresisttechnique. The performance of the reduced projection exposure techniqueis mainly determined by two fundamental quantities of resolution RP anddepth of focus DOP. Assuming that the exposure wavelength of aprojection optical system is λ and the numerical aperture of aprojection lens is N, the above fundamental quantities are representedas RP=k1λ/NA and DOP=k2λ/NA. In order to improve the resolution of thelithography, it is important to decrease the wavelength λ and increasethe numerical aperture NA of the projection lens.

[0005] In this case, if the NA is increased, the resolution is improved,whereas the depth of focus decreases in inverse proportion to the squareof NA. The tendency of micromachining was to decrease the exposurewavelength λ. Therefore, the exposure wavelength λ has been shortenedfrom g-line (436 nm) into a short wavelength of i-line (365 nm). Atpresent, the main tendency is an excimer laser (248 nm, 193 nm).

[0006] However, in the lithography using light, the diffraction limit oflight is the limit of the resolution. Therefore, it is said that evenwith the F2 excimer laser at 248 nm, the micromachining to the linewidth of 100 nm is the limit of the lithography using a lens seriesoptical system. Further, in order to acquire the resolution in the orderof magnitude of nanometer, the lithography of an electron beam or X-ray(particularly, SOR light: synchrotron radiation light) must be employed.

[0007] The electron beam lithography permits the pattern in the order ofmagnitude of nanometer to be controlled accurately, and provides muchgreater depth of focus than the optical system does. The electron beamlithography has an advantage that it can directly draw on a waferwithout using a mask. However, the electron beam lithography has adefect that it provides a low throughput and requires high cost and hasa long way to reach the level of mass production.

[0008] The X-ray lithography, in either equivalent exposure using a 1:1mask or a reflective imaging X-ray optical system, permits theresolution and accuracy to be improved by one order of magnitude ascompared with the exposure of excimer laser. However, the X-raylithography is problematic in that it is difficult to implement becauseof difficulty of making the mask and provides high cost of theapparatus.

[0009] In the lithography using the electron beam or X-rays, thephotoresist must be developed according to the exposure method. Thislithography is still problematic from the viewpoints of sensitivity,resolution, etching resistance, etc.

[0010] As a method for solving these problems, there has been proposed amethod of using, as a light source, proximity field light which oozesout from an aperture having a much smaller diameter than the wavelengthof light to be projected and exposing photoresist to light anddeveloping it to make a fine pattern.

[0011] This proposed method can provide the special resolution in theorder of magnitude of nanometer regardless of the wavelength of a lightsource.

[0012]FIG. 12 is views showing the method of duplicating a fine patternusing proximity field exposure.

[0013] As seen from FIG. 12(a), photoresist of a photosensitive materialis continuously applied to a substrate 31 by spin-coating or spraying toform a photoresist layer 33.

[0014] On the other hand, a mask 34 with a metallic minute pattern 36 ona mask substrate 35 of dielectric such as glass is prepared.

[0015] Next, as seen from FIG. 12(b), the mask 34 is brought intointimate contact with the photoresist layer 33 in such a way that thepattern 36 on the mask substrate 35 is opposite to the substrate 31.

[0016] As seen from FIG. 12(c), with the mask 34 superposed on thesubstrate 31, the rear surface of the mask substrate 35 is irradiatedwith the light 39 such as i-line (365 nm).

[0017] Then, as seen from FIG. 12(d), owing to the irradiation with thelight of the i-line, proximity field light 37 oozes out from theaperture free from the metal of the pattern 36. Thus, exposure is madeso that the corresponding portion h of the photoresist is exposed tolight.

[0018] After optical exposure, as seen from FIG. 12(e), the mask 34 istaken from the substrate 31. The photoresist layer 33 is developed usinga developing liquid. The portion h exposed to light is made soluble in adeveloping solvent, thereby forming a positive pattern.

[0019] Referring to a sectional view of an intimate-contact exposingapparatus using vacuum evacuation, an explanation will be given of amethod of intimate-contact exposure. First, a wafer with the photoresistlayer 33 applied on the substrate 31 is mounted on a stand of anexposure apparatus, and a mask 34 is mounted in contact with the wafer.

[0020] Before exposure, as seen from FIG. 13(a), an inert gas such as N₂is continuously caused to flow between the mask 34 and the photoresistlayer 33 within the apparatus. During the exposure, as seen from FIG.13(b), the space between the mask 34 and the photoresist layer 33 isvacuum-exhausted so that the mask 34 is brought into contact with thephotoresist layer 33. Thereafter, light 39 is projected from the rearsurface of the mask.

[0021] As seen from FIG. 13(c), the N₂ gas is caused to flow within theapparatus again so that the mask 34 is separated from the photoresistlayer.

[0022] Incidentally, in the above explanation, the photosensitivephotoresist of the photoresist layer 33 was a positive pattern in whichthe exposed portion is soluble in a development solvent. However, it maybe negative photoresist in which only the portion exposed to light isinsoluble in the development solvent.

[0023] The thickness of the photoresist layer is desired to be equal toor smaller than the oozing depth of the proximity field light.

[0024] The photoresist material used in the photoresist layer 33 ispreferably a material which can be developed in an aqueous alkalinedevelopment solution since it does not produce organic liquid wastes,provides less swelling and has high development capability to make agood pattern. More specifically, it may be pattern making materialcontaining silicon-containing polymer which is water-insoluble andalkali-soluble and photosensitive compound.

[0025] In this way, the method of proximity field optical exposurethrough collective exposure using the mask has been proposed which hashigh industrial utility value from the standpoint of throughput. In thiscase, the proximity field light has small optical strength equal to anaperture width so that the mask must be in contact with the photoresistas intimate as possible.

[0026] A contact aligner which has been conventionally employed alsoeffectively adopts a method of evacuating the space between the waferand the mask in order to improve the pattern size accuracy so that theyare brought into strong and intimate contact with each other.

[0027] However, in the above prior art, the exposure could beimplemented in intimate contact between the wafer and mask by vacuumexhaustion. However, this enhanced intimate contact between the waferand mask produces a problem of sticking that they cannot be separated.

SUMMARY OF THE INVENTION

[0028] In order to solve the problem of sticking, a method of improvingthe resist material was attempted. However, this method produced a maskdefect due to application of particles (dust). For this reason, in aconventional semiconductor process, projection exposure has beenadopted. However, in the proximity field exposure in which propagatinglight can be employed, the mask and the resist face must be necessarilybrought in intimate contact with each other. Therefore, the problem ofsticking is a great obstacle in practical use.

[0029] In order to solve this problem, a technique has been proposedwhich makes a mask using flexible resin (PDMS: polydimethylsiloxane) asa mask material (J. VacSci. Technol. B1681. 1998). This technique has anadvantage that the mask which is flexible and apt to deform can beeasily peeled from the resist. On the other hand, since the mask is aptto deform, while the mask is made and during the exposure, the size ofthe mask pattern is likely to vary. This makes the pattern accuracyproblematic. Particularly, the pattern employed for optical control suchas a DBR grating, which requires high pitch controllability in the orderof magnitude of nanometer, becomes problematic.

[0030] In the case of contact exposure, since the mask is repeatedlybrought into intimate contact with the wafer, likelihood of applicationof particles on the mask is strong. This requires mask cleaning.However, since the mask which is made of resin is low inchemical/physical resistance, a conventional cleaning technique cannotbe used.

[0031] Additionally, in order to avoid this problem, there has beenproposed a technique in which inversely to the above proposal, the waferis made as a membrene (thin film) to realize a pattern with minutepitches (Takahiko ONO and Masayoshi ESASHI, “Subwavelength PatternTransfer by Proximity Field Photolithography” Jpn. J. Appln. Phys. Vol.37(1998), pp.6745-6749, Part 1, NO. 12B, December 1998). However, thistechnique, which requires the wafer itself to be processed previously,is problematic in the freedom of selecting a material of wafer and thestrength of the wafer and hence is not practical.

[0032] In order to attain the above object, the invention described inthis invention is a mask for proximity field optical exposure wherein alight shading portion is formed so as to leave an aperture in aprescribed pattern on a surface of a mask body material that istransparent to exposure light, and the aperture as a patterning portionis subjected to proximity field optical exposure with being kept incontact with the surface of a wafer, said mask being made of atransparent material having a thickness of 1 mm or less.

[0033] Further, in this invention, a mask for proximity field opticalexposure is provided, wherein said mask has a thickness of 0.1 mm-0.5mm.

[0034] Further, in this invention, a mask for proximity field opticalexposure is provided, wherein said mask forms a circular shape.

[0035] Still further, in this invention, an exposure apparatus isprovided for performing proximity field optical exposure, comprising: amask having a light shading portion formed to leave an aperture in aprescribed pattern on a surface of a mask body material that istransparent to exposure light, and the aperture as a patterning portionbeing kept in contact with the surface of a wafer; a wafer chuck forkeeping a wafer opposed to the mask, and a pressure applying means forapplying stress to deform said mask.

[0036] Further, in this invention, an exposure apparatus according tothe above aspect, said pressure applying means applies stress to saidmask by lifting said mask.

[0037] Further, in this invention, an exposure apparatus according tothe above aspect, wherein said pressure applying means is provided witha gas blow-off means.

[0038] Further, in this invention, an exposure apparatus according tothe above aspect, wherein said pressure applying means has a handlerprovided with a fork inserting portion to be inserted between said maskand a mask holding means for holding the mask.

[0039] Further, in this invention, an exposure apparatus according tothe above aspect, wherein said mask is replaceable with another mask foreach exposure time.

[0040] Still further, in this invention, said exposure apparatusincludes a mask cleaning mechanism for cleaning the mask.

[0041] Further, in this invention, an exposure apparatus according tothe above aspect, wherein said mask cleaning mechanism is implemented inoxygen plasma or ozone ashing.

[0042] Further, in this invention, said mask cleaning mechanism hasscrubbers at both sides thereof respectively.

[0043] Further, in this invention, an exposure apparatus according tothe above aspects , wherein said exposure apparatus includes anautomatic inspection mechanism for automatically inspecting the cleaningstate of said mask.

[0044] Still further, in this invention, a proximity field opticalexposure method in which after a mask with a prescribed pattern isloaded on a mask chuck and a wafer with a photo-resist layer is loadedon a wafer chuck, said mask chuck and said wafer chuck are caused toapproach each other so that the pattern of said mask is brought intointimate contact with said photoresist layer of said wafer in order toimplement proximity field exposure, characterized in that after theexposure, a pressure applying means is caused to act on a peripheraledge of said mask so that said peripheral edge is elastically deformed,thereby starting peeling of the mask and wafer from each other.

BRIEF DESCRIPTION OF THE DRAWINGS

[0045] FIGS. 1(a)-1(d) show the sectional views showing the thickness ofa mask according to the first embodiment of this invention.

[0046] FIGS. 2(a) and 2(b) show the plan views showing the shapes of themask shown in FIGS. 1(a)-1(d).

[0047]FIG. 3 is a plan view of the wafer chuck shown in FIGS. 1(a)-1(d).

[0048] FIGS. 4(a) and 4(b) show the views each showing a mask liftingmechanism according to the second embodiment of this invention.

[0049]FIG. 5 is a view for explaining the peeling operation whencompressed air is used in place of the lifting member shown in FIGS.4(a) and 4(b).

[0050] FIGS. 6(a)-6(e) is the views showing the procedure of the peelingoperation in an exposure sequence of the exposure apparatus shown inFIGS. 4(a) and 4(b).

[0051] FIGS. 7(a)-7(c) show the views showing the procedure of thepeeling operation by gas jetting in the exposure apparatus shown inFIGS. 6(a)-6(e).

[0052] FIGS. 8(a)-8(d) show the views showing the peeling operation by astructure for the exposure sequence shown in FIGS. 6(a)-6(e).

[0053]FIG. 9 is a plan view of the structure shown in FIGS. 8(a)-8(d).

[0054]FIG. 10 is a block diagram of the exposure apparatus having anautomatic mask changer according to the third embodiment of thisinvention.

[0055]FIG. 11 is a block diagram of the exposure apparatus having a maskcleaning mechanism in place of the automatic mask changer shown in FIG.10.

[0056] FIGS. 12(a)-12(e) show the view showing the technique ofduplicating a minute pattern by proximity field exposure.

[0057] FIGS. 13(a)-13(c) show the sectional view of a contact exposureapparatus by vacuum evacuating.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0058] Now referring to FIGS. 1(a) to 11, an explanation will be givenof this invention.

[0059] First, referring to FIGS. 1(a)-1(d), the first embodiment of thisinvention will be explained.

[0060] FIGS. 1(a)-1(d) show the views for explaining the relationshipbetween the thickness of a mask and pressure. FIGS. 1(a) and 1(b)illustrate the case of the mask according to the first embodiment ofthis invention, and FIGS. 1(c) and 1(d) illustrate the case of aconventional mask.

[0061] In FIGS. 1(c) and 1(d), reference numeral 100 denotes aconventional mask. The conventional mask 100, which is made of amaterial with high degree of transparency, has no need of being formedas thin as possible. Rather, in order to prevent the mask from beingeasily broken by faint force, it was formed to have a thickness d2 whichis great as thick as 0.06 inch (1.5 mm) or more. Therefore, when stress400 is applied to the end of the mask so that the mask is peeled fromthe wafer 200, the stress 400 is dispersed like in FIG. 1(c) since themask has high rigidity, and hence must be very great.

[0062] Now, when the great stress 400 is applied, as seen in FIG. 1(d),an inconvenience occurred that the wafer 200 as well as the mask 100 ispeeled from a vacuum chuck 300 before the mask 100 is peeled from thewafer 200.

[0063] The applicant defeated the traditional common sense anddiscovered that the mask having a thickness d1 which is as thin aspossible can be peeled by faint force. Therefore, The applicantconfirmed that owing to faint force applied to the mask, less breakageof the mask in the exposure step is generated.

[0064] FIGS. 1(a) and 1(b) show the mask according to the firstembodiment of this invention. In FIGS. 1(a) and 1(b), reference numeral1 denotes a mask in which a metallic light-shading film is formed on asubstrate of glass or quartz/glass according to this invention.Reference numeral 2 denotes a wafer to be in intimate contact with themask 1. Reference numeral 3 denotes a wafer chuck for holding the wafer2. Reference numeral 4 denotes the stress by stress applying (peeling)means such as a pin for peeling the mask from the wafer 2.

[0065] The mask shown in FIGS. 1(a) and 1(b) are made of the material inwhich the metallic shading film is formed on the substrate ofquartz/glass like the conventional mask. The mask according to thisembodiment is characterized in that it has the thickness d1 of 1 mm orless, particularly 0.1-0.5 mm which is thinner than the conventionalmask. The mask which was made thin in this way can be easily elasticallydeformed. Where the wafer 2 is peeled from the mask 1 after exposure, asseen in FIG. 1(a), when faint force 4 is applied to the end of the mask1, the force is concentrated to that portion but not dispersed to theother portion. When the concentrated force exceeds the contact forcewith resist, that end will be peeled.

[0066] When the peeling at the end starts once, as seen in FIG. 1(b),the stress concentrated portion gradually shifts the contact area sothat the entire area will be peeled eventually.

[0067] In this way, in accordance with the first embodiment of thisinvention, since the mask 1 made thin can be easily elasticallydeformed, the mask can be easily peeled from the resist by faint force.It was confirmed that the mask is not broken within the above range ofthe thickness, and confirmed that the mask is likely to be broken with athickness d1 which is 0.1 mm or less.

[0068] Further, where particles exist on the wafer 2, the defective areacan be reduced by the elastic deformation of the mask 1 made thin.

[0069] Further, since the transparent member is made of quartz/glass,its deformation to stress/heat can be reduced as compared with resin.This permits the pattern to be made with high accuracy.

[0070] Referring to FIG. 2, the second embodiment of this invention willbe explained below.

[0071]FIG. 2 is a plan view for explaining the shape of the mask.

[0072]FIG. 2(a) shows the mask according to the second embodiment ofthis invention. FIG. 2(b) shows a conventional mask.

[0073] As seen from FIG. 2(b), the conventional mask 100 forms a squareshape. Where such a square mask 100 is peeled from the wafer 200 asshown in FIG. 1(b), with the stress 400 applied to the side area of themask 100, this area is difficult to deform and hence to be peeled.

[0074] On the other hand, the mask 1 according to the second embodimentof this invention forms a circular shape. Therefore, the sectionalsecondary moment when stress is applied to the edge of the mask 1 can bereduced. In addition, any position on the entire periphery is easilyelastically deformed by equal faint stress 4. The mask according to thisembodiment can be more easily peeled from the wafer than the squaremask.

[0075] A concrete example of the mask 1 will be explained.

[0076] First, quartz glass is molded into a wafer having a size of 4inch φ which is thereafter polished to have a thickness of 0.5 mm. A Crfilm having a thickness of 30 nm is deposited on the wafer by vacuumdeposition. Further, by common electron beam lithography, the mask 1with a minimum aperture having a width of 100 nm is manufactured.

[0077] Although depending on the means for applying the stress, wherethe compressed air (0.6 MPa) which is used as common pressurizing meansis used, the thickness d1 of the mask 1 is preferably 1 mm or less toprovide a deformation enough to peel. Where the mask is deformed withthe pressure of 0.3 MPa or so which is convenient to use, with thethickness of 0.5 mm or less, improved peel could be realized. Inversely,where the mask is made thin to have a thickness of 0.1 mm or less, thestrength is insufficient, thereby increasing the probability ofbreakage. This led to difficulty of handling such as polishing andcleaning in the manufacturing process described later.

[0078] Thus, it was confirmed that the mask thickness d1 of 0.1-0.5 mmis practically a range which permits the peeling and strength to becompatible.

[0079] Incidentally, in a step of applying resist on the wafer 2,photoresist is spin-coated on the wafer having a thickness of 0.4 mm and3 inch φ. In this case, the resist applied film is caused to have aminimum aperture width of a mask slit or less. With the mask aperturewidth of 100 nm, the resist film after baking was caused to have athickness of 50 nm. The mask pattern is brought into intimate contactwith the photoresist layer of the wafer thus formed. In such an intimatecontact state, the rear side of the mask substrate is irradiated withthe light of i-line. Owing to the light irradiation, the proximity fieldlight oozed out from the pattern aperture of the mask so that thephotoresist was exposed to light. After exposure, stress was applied tothe side area of the mask to deform the mask that the mask was peeledfrom the wafer.

[0080] The wafer 2 thus peeled was subjected to prescribed steps of PEB,development and drying, thus forming a resist pattern. The resistpattern actually formed has a pattern width of about 15 nm. Thus, by theproximity field optical lithography, the pattern whose width is largerthan the aperture but sufficiently narrower than the exposure wavelengthcould be formed.

[0081] Referring to FIGS. 3 and 4, the third embodiment of thisinvention will be explained.

[0082]FIG. 3 is a plan view showing a mask lifting mechanism of theexposure apparatus according to the third embodiment of this invention.FIG. 4 is a front sectional view of the state where a mask and a waferare loaded in the mask lifting mechanism of the exposure apparatus ofFIG. 3.

[0083] In FIG. 3, reference numeral 3 denotes a wafer chuck; 3 b anexhaust hole of the wafer chuck 3; 3 c an exhaust groove; 6 a masterchuck serving as a mask holding means; 6 a a mask chuck exhaust hole; 6c a mask chuck exhaust groove; and 5 a lifting pin of a mask liftingmember which is provided to be movable vertically with the mask chuckexhaust hole 6 a. The lifting pin 5 ascends when compressed air issupplied and descends when it is exhausted.

[0084] In FIG. 4, the other components of the mask lifting mechanism areas follows. Reference numeral 1 denotes a mask loaded on the mask chuck6; 2 a wafer loaded on the wafer chuck 3; 6 b an mask/wafer exhausthole; and 6 c an air supplying hole for driving the lifting pin 5.

[0085] An explanation will be given of the operation of the mask liftingmechanism of FIGS. 3 and 4.

[0086] As described above, the thin circular mask 1 which is apt todeform elastically according to the first and the second embodiment ofthis invention is placed on the mask chuck 6 shown in FIGS. 3 and 4. Byexhaustion from the mask exhaust hole 6 a, the mask 1 is firmly loadedon the mask chuck 6. On the other hand, the wafer 2 which is to beirradiated with proximity field light is placed on the wafer chuck 3. Byexhaustion from the wafer chuck exhaust hole 3 b, the wafer 2 is suckedby the wafer chuck exhaust groove 3 c so that it is firmly loaded on thewafer chuck 3. At the time of loading, as seen from FIG. 4(a), the maskchuck 6 and wafer chuck 3 are located apart from each other. During theexposure, the mask chuck 6 and the wafer chuck 3 are kept in contactwith each other.

[0087] After the exposure, as seen from FIG. 4(b), compressed air issupplied into the air supplying hole 6 c for driving the lifting pin 5.Thus, the lifting pin 5 is lifted upward so that the edge area of thedeformable mask 1 according to the first and the second embodiment islifted so as to deform. In this way, the mask 1 can be peeled from thewafer 2 easily and surely.

[0088]FIG. 5 shows an modification of the mask lifting mechanism of FIG.4 in which compressed air is used in place of the lifting pin 5. In FIG.5, reference numeral 1 denotes a mask loaded on the mask chuck 6; 2 awafer loaded on the wafer chuck 3; 6 b a mask/wafer exhaust hole; 3 awafer chuck; 3 a a seal of the wafer chuck 3; 3 b an exhaust hole of thewafer chuck 3; 3 c an exhaust groove of the wafer chuck 3; 6 a maskchuck serving as a mask holding means; 6 a a mask chuck exhaust hole; 6b a mask/wafer exhaust hole; 6 c a compressed air supplying hole; 7 acompressed air for lifting exhausted from the compressed air supplyinghole 6 c. In peeling, as seen from FIG. 5, the compressed air (or N₂gas) is sprayed between the wafer 2 and mask 1 so that the pressure thusgenerated peels the mask 1 and the wafer 2 from each other.

[0089] The mask lifting mechanism shown in FIG. 5, which does notrequire that the lifting pin 5 and its attaching space as shown in FIG.4 are machined, is convenient.

[0090] Referring to the drawings, an explanation will be given of theexposure sequence of the exposure apparatus according to this invention.

[0091] First, as shown in FIG. 6(a), with the resist applied Si wafer 2having a thickness and shape according to this invention set in thewafer chuck 3, when air exhaustion is effected from the wafer chuckexhaust hole 3 b, , the entire bottom of the wafer 2 is secured on thewafer chuck 3 by vacuum chucking through the exhaust groove 3 c shown inFIG. 3. On the other hand, with the mask 1 set in the mask chuck 6, whenthe air exhaustion is effected from the mask chuck exhaust hole 6 a, themask 1 is also secured by vacuum chucking.

[0092] Next, as seen from FIG. 6(b), with the wafer 2 and mask 1 alignedwith each other by alignment means (manipulator), while the spacebetween the mask 1 and wafer 2 is decompressed from the wafer/maskexhaust hole 6 b, the wafer chuck 3 is raised (or the mask chuck 6 islowered) so that the mask 1 and wafer 2 are caused to approach eachother and brought into contact with each other.

[0093] In this case, by decompression, the wafer chuck seal 3 a isbrought into contact with the bottom of the mask chuck 6 so that it isdeformed convexly upward (toward the wafer side) and the mask 1 isdeformed convexly downward (toward the wafer side). Thus, the remaininggas is expelled from the center of the wafer so that the degree ofcontact between the wafer and mask is improved (This effect isremarkable as the thickness of the mask decreases to increase thedeformation).

[0094] Thereafter, as seen from FIG. 6(c), before complete contact, thevacuum exhaust by the wafer chucking is released or the pressurizing isdone using N₂ gas, poor contact which is attributable to the sinking ofthe wafer in the chuck groove during the wafer chucking is reduced.

[0095] Finally, the surface of the wafer 2 is raised to be flush withthe lower surface of the mask 1. After the mask 1 is made horizontal,the wafer 2 is secured on the mask 1.

[0096] Upon completion of setting which is ready for exposure, by aproximity field optical exposure system using a high pressure mercurylamp (g, h, i lines), ultraviolet rays are applied during a prescribedtime. In this case, the applying direction is adjusted to providepolarized light in parallel to the slit direction of the mask 1.

[0097] Upon completion of the exposure, the wafer chuck 3 which has beenonce released is decompressed again to effect the vacuum chucking. Thedecompressed wafer/mask exhaust hole 6 b is released and the mask chuckexhaust hole 6 a is also released so that they are restored toatmospheric pressure. In this state, as seen from FIG. 6(d), the endarea of the mask 1 is lifted by the mask lifting pin 5 to peel the endof the wafer from the mask 1. Further, as shown in FIG. 6(e), the waferchuck 3 is lowered so that the entire wafer 2 can be peeled from themask 1.

[0098]FIG. 7 is a view for explaining the mask peeling mechanismaccording to the fourth embodiment of this invention.

[0099] In FIG. 7, reference numeral 1 denotes a mask loaded on the maskchuck 6; 2 a wafer loaded on the wafer chuck 3; 6 b a mask/wafer exhausthole; 3 a wafer chuck; 3 a a seal of the wafer chuck 3; 3 b an exhausthole of the wafer chuck 3; 3 c an exhaust groove of the wafer chuck 3; 6a mask chuck serving as a mask holding means; 6 a a mask chuck exhausthole; 6 b a mask/wafer exhaust hole; and 8 a gas blow-off tube. Theother components than the gas blow-off tube 8 have the same functions asthose of the corresponding components in the above mask peelingmechanism.

[0100] An explanation will be given of the operation of the mask peelingmechanism according to this embodiment of this invention.

[0101]FIG. 7(a) shows the state after the exposure has been completed.In FIG. 7(a), after the exposure, the gas blow-off tube is arranged atthe center of the mask 1.

[0102] Thereafter, as seen from FIG. 7(b), while the wafer chuck 3 islowered, the N₂ gas (which may be replaced by compressed gas) is jettoward the top of the mask 1 from the gas blow-off tube 8. Thus, thecentral portion of the deformable mask 1 according to this invention isdeformed downward so that a gap is produced between the mask 1 and wafer2. At the same time, if the air is supplied into the wafer chuck exhausthole 3 b and mask/wafer exhaust hole 6 b, the peeling can be effectedmore surely.

[0103] Further, when the wafer chuck 3 is lowered, as seen from FIG. 7c,the wafer 2 and the mask 1 can be peeled from each other.

[0104]FIG. 8 is a view for explaining the peeling procedure according tothe fifth embodiment of this invention in which a handler 9 as shown inFIG. 9 is employed. In FIG. 8, reference numeral 1 denotes a mask loadedon the mask chuck 6; 2 a wafer loaded on the wafer chuck 3; 6 b amask/wafer exhaust hole; 3 a wafer chuck; 3 a a seal of the wafer chuck3; 3 b an exhaust hole of the wafer chuck 3; 3 c an exhaust groove ofthe wafer chuck 3; 6 a mask chuck serving as a mask holding means; 6 a amask chuck exhaust hole; 6 b a mask/wafer exhaust hole; and 9 a handler.The other components than the handler 9 have the same functions as thoseof the corresponding components in the above mask peeling mechanism. Thestructure of the handler 9 is shown in a plan view of FIG. 9.

[0105] In FIG. 9, reference numeral 3 denotes a wafer chuck; 3 a a sealof the wafer chuck 3; 3 b an exhaust hole of the wafer chuck 3; 3 c anexhaust groove of the wafer chuck 3; 6 a mask chuck serving as a maskholding means; 6 a a mask chuck exhaust hole; 6 b a mask/wafer exhausthole; and 9 a handler. A mask 1 is indicated by dotted line. The handler9 includes tips 9 a and 9 b (hereinafter referred to as a tuning forkinserting portions) brunched in parallel from the base of the handlertoward the tip. The interval between the tuning fork inserting portions9 a and 9 b is slightly larger than the outer diameter of the waferchuck 3 and slightly smaller than the outer diameter of the circularmask according to this invention. Further, the depth of the space formedby the tuning fork inserting portions 9 a and 9 b is larger than theradius of the wafer chuck 3.

[0106] Referring to FIG. 8 again, an explanation will be given of theprocedure of the peeling operation using the handler 9 shown in FIG. 9.

[0107]FIG. 8 shows the state where the exposure has been completed.

[0108] Upon completion of the exposure, as shown in FIG. 8(b), the waferchuck 3 is raised upward from the sucking plane of the mask chuck 6.Further, the fork inserting portions 9 a and 9 b of the handler 9 shownin FIG. 9 are inserted in the gap between the mask 1 and mask chuck 6.

[0109] Thereafter, when the wafer chuck 3 is lowered and the mask 1 ispressed against the handler 9, as shown in FIG. 8(c), the mask 1 startto deform.

[0110] When the wafer chuck 3 continues to be lowered as it is, the mask1 and the wafer 2 are eventually peeled from each other as shown in FIG.8(d).

[0111] In this case, after the end of the wafer starts to be peeled, ifthe N₂ gas is blown into the gap between the wafer 2 and the mask 1, thepeeling can be made more easily.

[0112] An explanation will be given of the sixth embodiment of thisinvention.

[0113]FIG. 10 is a block diagram of the exposure apparatus having anautomatic mask changer according to the sixth embodiment of thisinvention.

[0114] In a conventional exposure apparatus, a single mask was set inthe mask chuck to process a plurality of wafers successively. However,in the proximity field lithography, since the exposure is made with thewafer 2 and the mask 1 being in contact with each other, the particlessuch as resist were applied to the mask. This led to deterioration ofthe contact and occurrence of pattern defects, thereby making itdifficult to put the proximity field lithography into practice. In orderto overcome such difficulty, in the sixth embodiment of this invention,the same number of masks 1 as the wafers 2 are prepared so that the mask1 is automatically replaced by another mask whenever the single wafer isexposed.

[0115] In the automatic mask changer shown in FIG. 10, reference numeral20 denotes an exposure unit which incorporates the exposure mechanism orpeeling mechanism shown in FIGS. 3 to 9. Reference numeral 21 denotes amask carrier which holds a plurality of masks as shown in FIGS. 1 and 2.Reference numeral 22 denotes a wafer carrier which holds a plurality ofwafers 2. Reference numeral 23 denotes a wafer transporting system or atransporting robot which transports the wafer 2 from the wafer carrier21 to the exposure unit 20 so that it is set in the wafer chuck 3 andafter exposure, takes it out. Reference numeral 24 denotes a masktransporting system or transporting robot which sets the mask 1 on themask carrier 21 in the mask chuck 6 and after exposure, takes it out.

[0116] An explanation will be given of the operation of the exposureapparatus having an automatic mask changer according to the sixthembodiment of this invention shown in FIG. 10.

[0117] Using the manipulator of the wafer transporting system 23, thewafer 2 on the wafer carrier 22 is caught and set on the wafer chuck 3of the exposure unit 20. Next, using the manipulator of the masktransporting system 24, the mask 2 in the mask carrier 21 is set on thewafer chuck 3 of the exposure unit 20.

[0118] The subsequent operation will be carried. For example, as seenfrom FIGS. 6(a) to (c), the mask 1 and wafer 2 are aligned with eachother, brought into intimate contact with each other and secured in theexposure unit 20.

[0119] Upon completion of the exposure, the mask 1 and the wafer 2 arepeeled from each other in the manner shown in FIGS. 6(d) to (e) and thepeeling means as shown in FIGS. 7 to 9.

[0120] Upon completion of the peeling, for example, the wafer 2 is takenout from the exposure unit 20 to the next step through the wafertransporting system 23. Otherwise, it is returned to the wafer carrier22 as the processed wafer to be stored. In this case, the second wafer 2is transported from the wafer carrier 22 and set on the wafer chuck 3(Incidentally it should be noted that the order of these operationshould not be limited).

[0121] Subsequently, the mask 1 is carried out from the exposure unit 20through the mask transporting system 24 and returned to the mask carrier21 the used mask to be stored. In this case, the second mask 1 istransported to the exposure unit 20 and set on the mask chuck 6. This issucceeded by the processing shown in FIG. 6 et seq.

[0122] In this case, since the mask 1 to be used forms the same circularshape as the common wafer 1, it can be employed without greatly changingthe conventional wafer transporting mechanism. This gives an advantageof reducing the apparatus cost.

[0123]FIG. 11 shows an exposure apparatus provided with a mask cleaningmechanism 25 in place of the automatic mask changer shown in FIG. 10.This embodiment permits the mask to be not changed but cleaned, and tobe used for a plurality of wafers.

[0124] In FIG. 11, reference numeral 25 denotes a mask cleaningmechanism which may be actually a plasma or ozone ashing apparatus, orscrubber apparatus for carrying out both-side blushing.

[0125] Reference numeral 26 denotes an inspecting unit for inspectingparticles to confirm the cleaning state of the mask 1. As the case maybe, this inspecting unit may be combined with the mask cleaningmechanism 25.

[0126] An explanation will be given of the exposure apparatus accordingto this embodiment shown in FIG. 11.

[0127] By the wafer transporting system 23 and the mask transportingsystem 24, the wafer 2 and the mask 1 are set on the wafer chuck 3 andmask chuck 6, respectively, and in this state, the exposure is carriedout.

[0128] Upon completion of the exposure, the wafer 2 is carried outthrough the wafer transporting system 23 and the second wafer is set onthe wafer chuck 3.

[0129] The mask 1 is transported to the mask cleaning mechanism 25through the mask transporting system 24 and subjected to a cleaningstep. Thereafter, the mask 1 is transported to the inspecting unit 26through the mask transporting system 24. The mask 1 is subjected to aparticle inspecting step by optical inspection by the inspecting unit26. If the inspection result is OK, the mask 1 is transported to theexposure unit 20 through the mask transporting system 24, and set on themask chuck 6 again.

[0130] If the inspection result is not OK, the mask 1 is returned to themask cleaning mechanism 25. The mask 1 is cleaned again and transportedto the inspecting step.

[0131] In this case, as the mask cleaning mechanism, the apparatus whichhas been employed as a conventional wafer process can be used. Thiscontributes to cost reduction.

[0132] The exposure apparatus has been explained hither to assuming thatthe mask 1 having a thickness of 0.1-0.5 mm and forming a circular shapeaccording to this invention is used. However, using an ordinary mask,the proximity field lithography can be carried out to provide highproduction yield. Therefore, the proximity field lithograph should notbe limited to the case where the mask forming the circular shapeaccording to this invention is used.

[0133] As understood from the description hitherto made, in accordancewith this invention, by reducing the thickness of the mask, the exposureprocess which is good in the contact between the wafer and the mask andthe peeling from each other can be realized without greatly changing theshape of the substrate.

[0134] Further, by reducing the thickness of the mask, also where thereare particles on the wafer, a defective area can be reduced by thedeformation of the mask.

[0135] By making the mask in the same circular shape as the wafer, themask can be easily deformed at the periphery of the wafer in contactwith the mask, and hence the mask can be easily peeled from the wafer.

[0136] Further, by making the mask in the circular shape, a conventionalwafer process apparatus can be employed in the process of making themask. This contributes to the cost reduction.

[0137] Further, by making the mask in the circular shape, the wafer andmask can be easily peeled from each in a manner of applying stress tothe mask using the lifting pin or compressed air. This solves theproblem of sticking.

[0138] Further, by providing the exposure with the automatic maskchanger or cleaning machine, reduction in the production yield due tomask contamination by the contact exposure can be avoided.

What is claimed is:
 1. A mask for proximity field optical exposurewherein a light shading portion is formed so as to leave an aperture ina prescribed pattern on a surface of a mask body material that istransparent to exposure light, and the aperture as a patterning portionis subjected to proximity field optical exposure with being kept incontact with the surface of a wafer, said mask being made of atransparent material having a thickness of 1 mm or less.
 2. A mask forproximity field optical exposure according to claim 1, wherein said maskhas a thickness of 0.1 mm-0.5 mm.
 3. A mask for proximity field opticalexposure according to claim 1 or 2, wherein said mask forms a circularshape.
 4. An exposure apparatus for performing proximity field opticalexposure, comprising: a mask having a light shading portion formed toleave an aperture in a prescribed pattern on a surface of a mask bodymaterial that is transparent to exposure light, and the aperture as apatterning portion being kept in contact with the surface of a wafer, awafer chuck for keeping a wafer opposed to the mask, and a pressureapplying means for applying stress to deform said mask.
 5. An exposureapparatus according to claim 4, wherein said pressure applying meansapplies stress to said mask by lifting said mask.
 6. An exposureapparatus according to claim 4, wherein said pressure applying means isprovided with a gas blow-off means.
 7. An exposure apparatus accordingto claim 4, wherein said pressure applying means has a handler providedwith a fork inserting portion to be inserted between said mask and amask holding means for holding the mask.
 8. An exposure apparatusaccording to claim 4, wherein said mask is replaceable with another maskfor each exposure time.
 9. An exposure apparatus according to claim 4,wherein said exposure apparatus includes a mask cleaning mechanism forcleaning the mask.
 10. An exposure apparatus according to claim 9,wherein said mask cleaning mechanism is implemented in oxygen plasma orozone ashing.
 11. An exposure apparatus according to claim 9, whereinsaid mask cleaning mechanism has scrubbers at both sides thereofrespectively.
 12. An exposure apparatus according to any one of claims 9to 11, wherein said exposure apparatus includes an automatic inspectionmechanism for automatically inspecting the cleaning state of said mask.13. A proximity field optical exposure method in which after a mask witha prescribed pattern is loaded on a mask chuck and a wafer with aphoto-resist layer is loaded on a wafer chuck, said mask chuck and saidwafer chuck are caused to approach each other so that the pattern ofsaid mask is brought into intimate contact with said photoresist layerof said wafer in order to implement proximity field exposure,characterized in that after the exposure, a pressure applying means iscaused to act on a peripheral edge of said mask so that said peripheraledge is elastically deformed, thereby starting peeling of the mask andwafer from each other.